The Agronomic Division of the N.C. Department of Agriculture and Consumer Services (NCDA&CS) conducted a two-year study to evaluate the effect of soil-applied potassium on yield of cotton (Gossypium hirsutum L.). Growers in North Carolina routinely make spring applications of potassium to cotton fields to ensure a high level of soil fertility. Historical NCDA&CS soil test data indicate that a cotton crop grown on a soil containing 176 ppm (soil K index 90) of Mehlich-3–extractable K does not require additional potassium. However, many growers continue to apply potassium to achieve “highest possible” yields.

The objective of this study was to determine whether additional potassium is justified. Three rates of potassium (0, 67,134 kg/ha) were applied in replicated plots at three locations having soil K indexes ranging from 70 to 95 in major cotton- producing areas of the coastal plain of North Carolina. Leaf tissue and petiole analyses were conducted weekly from early bloom through fifth week of bloom during the growing season to measure potassium levels within the crop. Mean petiole K values remained 4% or greater for each sampling period over the 2-year study. Overall average yields for the study were 1,006 kg/ha and 1,068 kg/ha for study years 2000 and 2001, respectively. Data indicate no response to soil-applied potassium at all locations. This study validates current NCDA&CS soil test recommendations for potassium applications to cotton.